1. Field of the Invention
This invention relates to a method and apparatus for automatic weld line tracing whereby a weld arc is accurately traced along a weld line with a groove by detecting the weld line by means of a non-contact type sensor.
2. Description of the Prior Art
A conventional automatic weld line tracing apparatus is shown in FIG. 1. In this drawing, reference numerals 1, 1' show base metals with a groove 2. Numeral 3 shows a welding torch, and numeral 4 a sensor. Both the welding torch 3 and the sensor 4 are mounted on a lateral carriage 5, which is mounted on a vertical carriage 6, which in turn is supported on a manipulator 7. Numeral 8 shows a control device, whereby the welding torch traces the groove 2 in response to the detection signal of the sensor 4.
This type of automatic weld line tracing apparatus has the problem of low tracing accuracy. For one thing, if the apparatus involves a contact-type sensor, it is largely affected by the conditions of the base metal surfaces in contact with the sensor, and the tracing operation greatly depends on tack weld or spattering. Further, the fact that the part of the sensor in contact with the base metals comprises a steel ball or roller poses the problem of lack of smooth mechanical motion sufficient for high tracing accuracy.
Non-contact types of sensor include those using electricity, magnetism or optics. All of them involve a large size of sensor and are of no practical use. Arc light, heat, fume, spatter, etc. at the time of welding operation further reduces the practicability. In addition, the torch is controlled only in lateral directions, often resulting in an error in actual tracing operation.